The hydra is a legendary beast most famous for its encounter with Heracles, the great Greek hero. The amount of heads can range from five to several hundred. This is because for every head one cuts off, another two replaces it. Heracles, however, was able to defeat the hydra by having his cousin burn the stumps, charring the skin and keeping the hydra from growing new heads. There is said, though, to be a central, immortal head that governs the other heads and the body. This was proven when it tried to take a snap at Heracles, but thankfully the hero buried it deep underground. Freshwater hydras, as the name suggests, live by bodies of fresh waters, such as lakes, rivers, and streams, and either make their lairs in caves above or below the surface of the water.
Saltwater hydras, however, are different in three aspects. One, obviously, is that they live in seas and oceans, preferably deep sea trenches. Two, saltwater hydras do not possess either venom or poisonous blood. And most importantly, three; saltwater hydras can grow up to hundres of feet long in the right conditions. Each head is capable of swallowing a decent sized vessel whole. They rise up without warning, causing tsunami sized waves and cause the sea to froth and boil. Some legends even claim they can start storms, and are the source of the famed nor'eastern squall. When they sink back down beneath the waves it makes a whirlpool so powerful, any remaining debris, and ships within several leagues, get sucked up into the deep for the hydra to eat at leisure. Thankfully, however, very few saltwater hydras remain in this world. Those that do are often content with sleeping soundly in the black abyss.